The invention relates generally to power-driven conveyors conveying articles and more particularly to conveyor systems using viscoelastic dampers and methods for smoothing conveyor belt motion.
One purpose of a conveyor, such as a conveyor belt, is to transport products or persons smoothly, either through a larger device or from one point to another in a manufacturing, logistic, or transport operation. Smooth, linear motion of the conveyor is important in many applications, such as, for example, transporting passengers, manufacturing extrusions, and conveying unstable products subject to tipping upright. But many variables cause the motion of conveyor belts not to be smooth. These variables include, but are not limited to, fluctuations in the belt's drive train, resonances in the conveyor belt, resonances in other coupled systems, and fluctuating loading caused by people walking over the surface of the belt. The fluctuations and resonances affect the conveyor belt's forward motion by causing speed changes, i.e., accelerations, which can jostle passengers, topple cans or bottles, or degrade a continuous manufacturing process. This problem is particularly evident in long conveyor systems because the accumulated elasticity of the long belt makes it difficult to control the belt's dynamic motion, which is mainly in the direction of belt travel for a moving belt. In people movers, for example, as a passenger walks or moves about on top of the belt, his shifting foot weight sets up a periodic load that acts as a forcing function. The spring constant of the long belt allows the belt to expand and compress to a degree that is noticeable and objectionable to the passenger on the belt. The dynamic motion of the belt becomes problematic. While shifting foot weight is the cause of the forcing function in this example, long belts are more elastic and more subject to resonance. Thus, there is a need for smoothly moving belt conveyors.